The present invention relates generally to spark plugs for igniting fuel/air mixtures and, more particularly, to a silent discharge plasma ignition apparatus. The invention was made with government support under Contract No. W-7405-ENG-36 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
A "lean-burn" engine is one that uses a stoichiometric fuel-air mixture. That is, a mixture is introduced into the cylinders where there is exactly sufficient oxygen present to oxidize the fuel completely. Currently, much richer mixtures are employed in vehicles. One reason for this relates to the fuel/air mixing process itself; that is, no known mixing process can thoroughly mix gases at the molecular level, especially when the turbulence is as low as it is for engine speeds at idle. Stratification generally occurs, and for a stoichiometric mixture, a single spark, albeit one having long duration, is insufficient to ensure formation of a stably propagating flame front. This results in engine misfires; an engine which is running "rough."
Alternative ignition systems employ multiple pulse drivers to drive conventional spark plugs. However, only a few pulses are generated per cylinder firing cycle, and the plugs fire at the same location for each pulse.
Barrier-discharge cells having an electrode gap of several millimeters and operating at ambient pressure generate microdischarges which are distributed uniformly (spatially and temporally) throughout the cell's discharge volume. See, e.g., Baldur Eliasson et al., "Nonequilibrium Volume Plasma Chemical Processing," IEEE Transactions on Plasma Science 19, no. 6, 1063-1077 (1991); and Manabu Higashi et al., "Soot Elimination and NO.sub.x and SO.sub.x Reduction in Diesel-Engine Exhaust by a Combination of Discharge Plasma and Oil Dynamics," IEEE Transactions on Plasma Science 20, no. 1, 1-11 (1992). Such cells are used in plasma chemistry where the discharge spatial density is important to ensure uniform chemistry throughout the gas mixture. An example is the industrial production of ozone for municipal water treatment. It is undesirable to operate these cells significantly above ambient atmospheric pressure, since the microdischarge spatial density becomes increasingly nonuniform with increase in pressure.
Accordingly, it is an object of the present invention to provide a high discharge volume, multiple microdischarge ignition system.
Another object of the invention is to provide an ignition system having self-terminating microdischarges.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.